Polygalacturonase
Encyclopedia
Polygalacturonase is an enzyme
produced in plants which is involved in the ripening process, and by some bacteria and fungi which is involved in the rotting process. PGs degrades polygalacturonan present in the cell walls of plants by hydrolysis
of the glycosidic bonds that link galacturonic acid residues. Polygalacturonan is a significant carbohydrate component of the pectin
network that comprises plant cell walls. The activity of the endogenous plant PGs work to soften and sweeten fruit during the ripening process. Similarly, phytopathogens use PGs as a means to weaken the pectin network, so that a host of digestive enzymes can be excreted into the plant host to acquire nutrients.
has been used to determine the three-dimensional structure of several PGs. Fungal PGs from Collectotrichum lupine, Aspergillus aculeatus
, and Aspergillus niger
(PG1 and PG2) have been crystallized. The PG from Erwinia carotovora
is the crystallized bacterial PG. Because of the significant role PGs play in agriculture and industry, computational molecular modeling has been applied to generate theoretical structures of other important PGs. The experimentally determined crystal structures are used as templates for the computational threading process.
proteins that have been reported to demonstrate both competitive and non-competitive inhibition of PGs. The crystal structure has been determined for one plant PGIP, PGIP2 from Phaseolus vulgaris (bean). The theoretical structures of other PGIPs have been determined for some other common crops, using PGIP2 as the template.
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
produced in plants which is involved in the ripening process, and by some bacteria and fungi which is involved in the rotting process. PGs degrades polygalacturonan present in the cell walls of plants by hydrolysis
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
of the glycosidic bonds that link galacturonic acid residues. Polygalacturonan is a significant carbohydrate component of the pectin
Pectin
Pectin is a structural heteropolysaccharide contained in the primary cell walls of terrestrial plants. It was first isolated and described in 1825 by Henri Braconnot...
network that comprises plant cell walls. The activity of the endogenous plant PGs work to soften and sweeten fruit during the ripening process. Similarly, phytopathogens use PGs as a means to weaken the pectin network, so that a host of digestive enzymes can be excreted into the plant host to acquire nutrients.
Structure
X-ray crystallographyX-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
has been used to determine the three-dimensional structure of several PGs. Fungal PGs from Collectotrichum lupine, Aspergillus aculeatus
Aspergillus aculeatus
Aspergillus aculeatus is a plant pathogen.- External links :* *...
, and Aspergillus niger
Aspergillus niger
Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It causes a disease called black mold on certain fruits and vegetables such as grapes, onions, and peanuts, and is a common contaminant of food...
(PG1 and PG2) have been crystallized. The PG from Erwinia carotovora
Erwinia carotovora
Pectobacterium carotovorum is a bacterium of the family Enterobacteriaceae, which is a plant pathogen with a diverse host range. It causes soft rot and blackleg of potato and vegetables as well as slime flux on many different tree species....
is the crystallized bacterial PG. Because of the significant role PGs play in agriculture and industry, computational molecular modeling has been applied to generate theoretical structures of other important PGs. The experimentally determined crystal structures are used as templates for the computational threading process.
Inhibition
Most plants have inhibitor proteins against some PGs. The polygalacturonase inhibitor proteins (PGIPs) are leucine-rich repeatLeucine-rich repeat
A leucine-rich repeat is a protein structural motif that forms an α/β horseshoe fold. It is composed of repeating 20–30 amino acid stretches that are unusually rich in the hydrophobic amino acid leucine...
proteins that have been reported to demonstrate both competitive and non-competitive inhibition of PGs. The crystal structure has been determined for one plant PGIP, PGIP2 from Phaseolus vulgaris (bean). The theoretical structures of other PGIPs have been determined for some other common crops, using PGIP2 as the template.